Power processing systems are used to provide electrical power to a broad variety of applications, from automobiles to zeppelins. In many if not all of these applications, the size and mass of the power processing system are among the first design considerations. For most power processing systems, overall size and mass are typically determined by magnetic components, such as transformers and inductors. If these magnetic components can be made smaller and lighter, then the overall systems in which they are included become smaller, lighter, and usually less expensive.
In turn, for both transformers and inductors, size and mass are generally based on thermal considerations. That is, as heat transfer is improved, size can be reduced, because winding current densities and core voltage can increase without excessively raising the temperature. Accordingly, substantial effort has been directed toward achieving efficient heat transfer between the winding and ambient and between the core and ambient.
In many conventional power processing systems, magnetic components are cooled by free-convection or forced-air cooling. In these systems, heat transfer is limited by the heat transfer coefficient of air, which is typically in the range of 0.4 to 0.8 mW/cm2/° C. for free convection and 1.0 to 3.0 mW/cm2/° C. for forced-air cooling.
In other conventional power processing systems that utilize liquid cooling (e.g., transformer oil), the heat transfer coefficient is typically improved by more than a factor of ten. While this enables the associated magnetic components to be significantly reduced in size, the inconvenience and economic cost of providing the liquid coolant flow frequently offsets this performance advantage. Furthermore, in cases where the coolant contacts only the outer surface of the winding, thermal resistance of the winding itself may become the limiting factor.
In power systems rated above about 50 kW, cooling the system frequently involves a cold-plate, which may be either forced-air or liquid-cooled. In such cases, a low thermal impedance path is desired between both the winding and the core to the cold plate. One of the key challenges in obtaining the low thermal impedance path is the relatively poor thermal conductivity of electrical insulation materials in the winding. Accordingly, any design which involves heat transfer to a base-plate should have relatively short heat flow paths through the electrical insulation.
In various systems including power processing systems, a potting material or other encapsulant is frequently used to encapsulate various types of components, as is well known to those skilled in the art of electrical and electronic packaging. One conventional method of potting includes the use of a potting cup, a mold, or some other vessel, into which the components to be protected are placed, and an encapsulant or potting compound such as an epoxy or resin is poured or injected into the vessel to cover the components. The potting compound is then cured and hardened. Such a potting compound can provide the internal components with varying degrees of protection from environmental contamination, electrical insulation, structural support, and a thermally conductive path from the component to ambient.
However, further improvement in the conduction of heat away from power processing systems and various other electrical and electronic components is desired.